1. Field Of The Invention
The present invention relates to a rotational type variable resistor having a plurality of resistor lamination layers and in particular to a resistor of the type wherein a brush slides over the surface of the resistor lamination layers to produce a linear change in resistivity.
2. Description Of Related Art
An apparatus for a variable resistor of this type is disclosed in Japanese Kokai publication No. 63-182509. FIGS. 6, 7 and 8 of the present application show the variable resistor of this publication. The above-mentioned variable resistor has a base plate 50. A first lead portion 51, second lead portion 52 and an electrode 53 are defined on the surface of the base plate. The first and second lead portions 51, 52 and the electrode 53 made of copper foil are formed through an etching process. As shown in FIG. 7, an arc shaped first resistance layer 54, which is shown as a shaded portion, is laminated between the first lead portion 51 and the second lead portion 52. The first resistance element layer 54 is directly formed on the base plate 50. Likewise, a first resistance element layer 54' which is shown as a shaded portion is laminated on the surface of the electrode 53. The raw material of the first resistance layers 54,54 is a heat fusible carbon paste The electrical resistance of the first resistance layer 54 is 350 ohms per square cm of substrate. As shown in FIG. 8, a second resistance element layer 55 (double shaded portion) is laminated only on the surface of the first resistance layer 54. The raw material of the second resistance layer 55 is a heat fusible carbon paste. The electrical resistance of the second resistance element layer 55 is 3K ohms per square cm of substrate.